1. Field of the Invention
This invention involves matrix isolation thin films and the reflective containment of electromagnetic radiation in such films for purposes such as spectroscopic studies of the film material, and the stimulation of reactions between various film constituents.
2. Description of the Prior Art
Over the past century, spectroscopic techniques have provided invaluable information on the detailed structure of atoms and molecules and their various interactions. Atoms and small molecules may be studied relatively easily while in the vapor state, and under certain circumstances, even in the solid state. Under these experimental conditions, the spectra associated with systems under study are sufficiently clear to be analyzed in detail thereby yielding important information on the physical characteristics of the systems under study. However, more complicated molecules, of larger size or of sophisticated structure, yield highly involved spectra whose analysis becomes more and more difficult, and for certain systems impossible, even with the use of sophisticated computer instrumentation. The spectra of such systems are complicated not only by the inherently detailed nature of the spectra of the individual molecules, but are further complicated by spectral characteristics associated with thermal motion and interactions between various groups of molecules.
During the past twenty-five years, the field of matrix isolation spectroscopy has developed into a powerful tool to analyze complicated, or highly reactive, molecular systems. The matrix isolation technique generally involves freezing, in the form of a thin film, a rarefied mixture of the material to be studied and an inert gas. The frozen thin film of this mixture is then analyzed using basic prior art optical techniques, e.g., exposure of the sample to irradiating electromagnetic radiation, and analysis of the resultant transmitted or scattered light. In this matrix configuration, the spectroscopic effects of thermal motion are essentially removed by virtue of the very low temperature of the frozen sample, e.g., on the order of 4 degrees Kelvin, or as low as possible. Furthermore, on a microscopic scale, the frozen sample appears as isolated molecules of the substance to be studied, frozen in the inert gas which acts as a host lattice. In this configuration, the molecules can be studied as isolated entities, thereby minimizing the spectroscopic complications associated with interactions between the guest and its environment (hence, the term "matrix isolation").
The thin films of the guest-host mixture are produced by directing a stream of appropriate guest-host vapor toward a cold substrate. The resultant thin film forms a guest-host lattice amenable to spectroscopic analysis. The irradiating light is directed towards the thin film and the resultant scattered light may be studied, or the transmission through the thin film may be analyzed, to obtain spectroscopic information relating to the molecules under study. Practical film sizes, however, are on the order of 100 microns, and light, either scattered off the 100 micron film or transmitted through the 100 micron film, yields only a very small signal, which must be treated with sophisticated electronics before it can provide meaningful information. Many systems are not amenable to analysis by matrix isolation spectroscopy because of the very small signal which is obtained. Various techniques are constantly being suggested to increase signal levels associated with matrix isolation spectroscopy, but none of these have yielded the type of improvement which would expand significantly the number of systems amenable to the matrix isolation technique.
In a totally unrelated art, thin films have been suggested as appropriate media for waveguide transmission of optical and infrared electromagnetic energy. Associated work has proposed the use of optical fibers as waveguides, and fiber lightguides have developed into the primary long distance optical transmission medium. However, interest in thin film waveguides has persisted since they are more readily used in integrated optical circuitry. The thin film waveguide generally comprises a center region where most of the optical radiation is transmitted, and outer regions of lower index of refraction where progressively less electromagnetic radiation is transmitted. This variation in index of refraction is fundamentally responsible for the guiding nature of the thin film. Significant efforts have been expended in learning how to fabricate films with appropriate index of refraction configurations so as to enhance the waveguiding properties of the thin film.
The development of thin film waveguide technology for use in information transmission systems has stimulated the use of such waveguides in experimental research directed toward the study of materials through optical means. Exemplary of this area of study is an article by Y. Levy, et al, in Optics Communications Vol. 11, No. 1 at page 66. These authors suggest studying various materials by forming a thin film waveguide of the material under study, irradiating the thin film waveguide with appropriate optical radiation which is sent through the film in various waveguide modes, and studying the resultant raman scattered light. It must be emphasized, however, especially with a view toward the invention described in this application, that work, such as that described by Levy, et al, depends on the formation of a "classical" thin film waveguide. Specifically, the thin film must have associated with it a core region of higher index of refraction than the surrounding "cladding" regions. (The prism device employed by these authors, which couples the probing laser into the waveguide mode, functions only when such a "classical" waveguide structure is used.)